The present invention relates generally to integrated circuits and methods of manufacturing integrated circuits. More particularly, the present invention relates to forming a metal interface layer between silicon nitride and copper.
In general, as semiconductor devices or integrated circuits have become smaller, the corresponding current densities across the metal conductors in the devices have increased. Metal conductors typically have an upper current density limit imposed by the phenomenon of electromigration. For example, aluminum conductors experience electromigration problems at current densities of approximately 105 amperes per square centimeter (A/cm2).
Electromigration refers to the transport of mass in metals due to the electric current. Electromigration is caused by the transfer of momentum from the electrons associated with the electric current to the positive metal ions. When a significant amount of current passes through thin metal conductors in semiconductor devices or integrated circuits, the metal ions associated with thin metal conductors are transported and tend to accumulate in some regions and be removed from other regions. The accumulation or pileup of the metal ions can short circuit adjacent conductors in the device. The removal of metal ions in other regions may create voids which result in an open circuit. Short circuits and open circuits caused by electromigration often result in device failure.
Electromigration failures have been described by Stanley Wolf, Ph.D. in Silicon Processing for the VLSI Era, Lattice Press, Sunset Beach, Calif., Vol. 2, pp. 264-65 (1990). Dr. Wolf explains that a positive divergence of the motion of the ions of a conductor leads to an accumulation of vacancies, forming a void in the metal. Such voids may ultimately grow to a size that results in open-circuit failure of the conductor line.
Integrated circuits typically include multiple layers of conductive lines separated by dielectric layers. These layers of conductive lines are typically referred to as metal layers (e.g., metal 1, metal 2, metal 3, etc.) and the dielectric layers are typically referred to as interlevel dielectric layers (ILD0, ILD1, ILD2, etc.). Copper lined films are being considered for use in metal layers due to their resistivity and resistance to electromigration.
Conductive lines and metal layers are discussed in U.S. Pat. Nos. 5,646,448; 5,770,519; and 5,639,691; each of which are assigned to the assignee of the present application. Generally, barrier layers are utilized with copper containing conductive structures to prevent copper diffusion into silicon substrates and insulative layers. Copper diffusion into silicon substrate degrades device integrity (xe2x80x9cpoisonxe2x80x9d the device) as well as the copper structure. Similarly, copper diffusion into insulative structures degrades performance of the insulative layers, as well as the copper structure.
Conventionally, barrier layers, such as silicon nitride have been utilized between the copper structure and the substrate and insulative layer. However, the interface between the silicon nitride material and the copper structure can be poor if the silicon nitride material is not processed properly. For example, chemical vapor deposited (CVD) silicon nitride must be pre-treated to ensure a proper interface. CVD silicon nitride without pre-treatment results in a poor Cu/SiN interface and possible delamination of the copper from the silicon nitride. Delamination creates a path from which copper ions can diffuse outward and to which moisture and other contaminates can diffuse inward. U.S. Pat. No. 6,271,595 discusses compounds which can be applied to copper surfaces to increase adhesion between copper and silicon nitride.
Thus, there is a need for an improved interface adhesion between silicon nitride and copper. Further, there is a need for a method of forming a metal interface layer between silicon nitride and copper. Even further, there is a need for a method of adding a metal organic precursor before silicon nitride chemical vapor deposition (CVD) to improve the silicon nitride interface.
An exemplary embodiment is related to a method of forming a metal layer interface between a copper layer and a silicon nitride layer. This method can include providing a metal organic gas over a copper layer, forming a metal layer from reactions between the metal organic gas and the copper layer, and depositing a silicon nitride layer over the metal layer and copper layer. The metal layer can provide an interface adhesion between the silicon nitride layer and the copper layer.
Another exemplary embodiment is related to a method of improving a silicon nitride and copper interface using added elements. The method can include providing a copper layer over an integrated circuit substrate, depositing added elements in a metal organic gas over the copper layer where the added elements react to copper in the copper layer and form a metal layer on top of the copper layer, and depositing silicon nitride over the metal layer and copper layer.
Another exemplary embodiment is related to a method of forming a via in an integrated circuit. This method can include depositing a copper layer, depositing an etch stop layer over the copper layer, depositing an insulating layer over the etch stop layer, forming an aperture in the insulating layer and the etch stop layer, depositing added elements in a metal organic gas over the copper layer where the added elements react to copper in the copper layer to form a metal layer on top of the copper layer, and depositing silicon nitride over the metal layer and copper layer.
Other principle features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.